This invention relates generally to the field of fluid filters, and, more particularly, to a filter for removing very small particles from fluids.
A filter is a device through which fluids such as liquids or gases are passed to remove matter suspended in the fluid. One common example is the oil filter of an automobile, through which the liquid oil is passed to remove suspended pieces of dirt, carbon, or other substances before the oil is recirculated to the engine. The particles are removed because they increase the friction and wear on the engine and thereby decrease its life. Similarly, the air to be combusted in an automobile engine is passed through its air filter to remove particles in the air, and the gasoline is also passed through a filter to remove particles therein. Most other types of fluids to be used in critical applications are also filtered in filters specialized to those particular needs.
The most common approach to filtering particles from fluids is to pass the fluid through a porous solid medium, called a filter element, having openings of the porosity that are too small to permit harmful particles to pass. The undesirable particles are thereby trapped on the filter element, which is periodically cleaned or replaced when it becomes dirty with trapped particles.
Paper or wire screen filter elements are widely used, but have significant drawbacks when employed in critical applications wherein the filter is subjected to high temperature or high levels of vibration, or where the filter is inaccessible so that a failure of the filter would be disastrous. For example, filters are used in the fuel and oxidizer lines of rockets and spacecraft to remove any particles suspended in the fluid before it is passed into the valves of the propellant system and into the rocket engine. Should there be a failure of the filter element in such an application, small particles or pieces of the failed filter may find their way to the valves of the propellant system and become deposited on valve seats. The small particles or pieces of filter material on the valve seats prevent the valves from sealing fully in a closed position, endangering the entire spacecraft operation.
Conventional paper or wire filters are particularly susceptible to such failures when designed to remove very small particles. Paper or plastic filters such as millipore filters can remove very small particles, but have filter elements that are mechanically weak and subject to degradation by high temperature or vibration. Wire screen type filters require the use of very fine wires if the particles to be removed are small, on the order of about 10 micrometers in diameter or smaller. Such fine wires are more likely to fail than are coarser wires, with the result that bits of the wire filter element may flow into and damage the propellant system.
Because such filter failures can result in extensive loss, rugged filters have been developed to withstand adverse conditions. In one type of such filter, a filter element is constructed by chemically etching channels into one flat surface of a flat annular ring of solid metal, leaving periodic supports unetched. The filter elements are stacked one against the other so that the supports of one filter element fit against the back side of the next filter element, leaving fluid conduits in the etched portions. The fluid flows through these rings and into the central cavity for collection, so that particles larger than the height of the channels are excluded and thereby cleansed from the fluid.
This type of rugged filter has no thin, weak portions that can be readily broken off or dislodged, and has gained acceptance in many critical applications. While providing acceptable service in filtering particles larger than about 10 micrometers in size, such filters are not generally available for filtering particles of a size less than about 10 micrometers.
There are no rugged filters generally available for filtering particles of less than about 10 micrometers, and certainly no rugged filters available for filtering particles of less than one micrometer in size. A need exists for such filters, for use in spacecraft and other industrial and commercial applications. The present invention fulfills this need, and further provides related advantages.